So on page 17, in the attack resolution steps, it shows you roll the attack dice, then "Apply attack dice rerolls: If either player has effects that would cause Attack dice to be re-rolled, they are applied now..." this implies that you roll the dice once, and reroll ONCE (if the attacker has rerolls, they would likely reroll the misses, and if the defender has rerolls, they would reroll the hits) essentially causing all the dice to be rerolled. This implies that any die can only be rerolled once. (there aren't two steps listed, attacker gets rerolls, defender gets rerolls, etc.)
However, on page 22 there is a Re-Rolls section that says "If both players have an effect that would cause a die to be rerolled, the player whose turn it is will first declare and utilize their effects. Once the new results have been generated, their opponent may opt to utilize their effects that would force rerolls" This seems to imply the attacker can reroll, but then the defender can reroll the rerolls (essentially trumping the attacker's rerolls) which appears to be in direct conflict with the rules on page 17.

So, which is it? can you only reroll any die once? or do the active player's rerolls have to go first, and therefore get trumped by their opponent's rerolls?

There's even a strange bit of wording on the page 22: "If both players have an effect that would cause /A DIE/ to be rerolled..." however, the attacker would not reroll the dice that rolled hits, and the defender would not reroll dice that are already misses... so... essentially there will never be a time when both players have an effect that would cause any particular die to be rerolled...

It would make the gameplay faster, and make more sense, if no die can even be rerolled more than once, however, I do see the argument for both sides, with the current written rules.